This invention relates to aqueous metal working fluids comprising of water and a mist suppressing copolymer. Optionally, the fluid may be an oil-in-water emulsion. Such emulsions include oil and an emulsifier. In addition to the mist suppressing copolymer, metal cutting operations often involve a work piece which rotates at relatively high speed, and a cutting tool both of which are lubricated by a metal working fluid. Under these high shear conditions, the metal working fluid is frequently thrown from the surface of the metal in the form of droplets. Often the droplets are small enough to be classified as a mist. Misting, or the formation of a mist is considered undesirable, because it represents a loss of the cutting fluid, and the cutting fluid mist is considered a contaminant in the air around the cutting machine.
Polymers containing acrylamides are known to thicken aqueous materials.
U.S. Pat. No. 5,089,578 discloses novel hydrophobically associated terpolymers containing sulfonate functionality which are useful as aqueous fluid rheology or flow control modifiers. The water soluble monomers are acrylamide and a salt of an ethylenically unsaturated sulfonic acid and the water insoluble monomer is a higher alkyl acrylamide. The ethylenically unsaturated sulfonic acids include materials such as sodium 2-acrylamido-2 methylpropane sulfonate. The mole percentage of acrylamide is preferably 5 to 98, more preferably 10 to 90 mole percent, the mole percentage of the salt of the sulfonate containing monomer is preferably from 2 to 95, and the mole percentage of the hydrophobic monomer is preferably from 0.1 to 10.0, more preferably 0.2 to 5 mole percent.
Acrylic polymers are used to control misting in metal working applications.
U.S. Pat. No. 4,493,777 discloses substantially oil free aqueous industrial fluids possessing superior lubricating and wear preventing characteristics which are useful as hydraulic fluids and metal working compositions. The fluids of the invention comprised one (1) an aqueous liquid and (2) a water soluble synthetic addition copolymer of (a) an ethylenically unsaturated cross-linking monomer, (b) an ethylenically unsaturated water soluble monomer and (c) an ethylenically unsaturated water insoluble monomer. The water soluble monomers include acrylamido-2-methylpropane sulfonic acid. Water insoluble monomers include styrene compounds, vinyl esters and acrylate esters. The cross-linking monomers are polyvinyl compounds which are present in amounts sufficient to control the degree of swellability of said copolymerization product, while imparting mechanical reinforcement to said copolymerization product.
International Patent WO 93/24601 discloses clear water-soluble polymer compounds having mean molecular weight higher than 1 million and selected among the polyalkylene oxides, polyacrylamides, polymethacrylamides, and the copolymers of an acrylamide and/or methyl acrylamide with unsaturated organic carboxylic acids having three (3) to five (5) carbon atoms, which are used in water-miscible and water mixed cooling lubricants, to reduce mist formation.
Polymeric anti-misting additives reduce the misting of machine fluids at the source by stabilizing them against break-up during the extreme shear conditions which occur during metal working operations. High molecular weight poly(ethylene oxide) is commonly used in this application. A typical polymer is POLYOX.RTM. available from Union Carbide. Typically, these polymers have a molecular weight from 1 to 2 million. However, these polymers are susceptible to shear. Metal working application often involve high shear, and as a result, metal working fluids containing high molecular weight poly(ethylene oxide) often suffer in performance when subjected to shear. Such degradation results when high shear conditions cause high molecular weight poly(ethylene oxide) to break down and lose its ability to suppress mist formation. In such high shear applications, the polymer must be replenished frequently.